Mo. Rev. Stat. § 300.475

In the event a highway includes two or more separate roadways and traffic is restricted to one direction upon any such roadway, no person shall stand or park a vehicle upon the left-hand side of such one-way roadway unless signs are erected to permit such standing or parking. The city traffic engineer is authorized to determine when standing or parking may be permitted upon the left-hand side of any such one-way roadway and to erect signs giving notice thereof.